Currently no vaccine exists for hepatitis C virus (HCV), a major pathogen thought to infect 170 million people globally. Many studies suggest that host T cell responses are critical for spontaneous resolution of disease, and preclinical studies have indicated a requirement for T cells in protection against challenge. We aimed to elicit HCV-specific T cells with the potential for protection using a recombinant adenoviral vector strategy in a Phase I study of healthy human volunteers. Two adenoviral vectors expressing NS proteins from HCV genotype 1B were constructed based on rare serotypes (Human Adenovirus 6 (Ad6) and Chimpanzee Adenovirus 3 (ChAd3)). Both vectors primed T cell responses against HCV proteins; these T cell responses targeted multiple proteins and were capable of recognizing heterologous strains (genotypes 1A and 3A). HCV-specific T cells consisted of both CD4+ and CD8+ T cells subsets, secreted IL-2, IFNγ, and TNFα, and could be sustained for at least a year after boosting with the heterologous adenoviral vector. Studies using MHC peptide tetramers revealed long-lived central and effector memory pools that retained polyfunctionality and proliferative capacity. These data indicate that an adenoviral vector strategy can induce sustained T cell responses of a magnitude and quality associated with protective immunity, and open the way for studies of prophylactic and therapeutic vaccines for HCV.

Abstract* "This manuscript has been accepted for publication in Science Translational Medicine. This version has not undergone final editing.Please refer to the complete version of record at www.sciencetranslationalmedicine.org/. The manuscript may not be reproduced or used in any manner that does not fall within the fair use provisions of the Copyright Act without the prior, written permission of AAAS."To whom correspondence should be addressed: ellie.barnes@ndm.ox.ac.uk E Barnes Peter Medawar Building, South Parks Rd, Oxford, UK OX1 3SY . + joint author contributions Author contributions: E.B., S. Capone, S. Colloca, J.H., A.F., R.C., C.K., A.N., and P.K. designed the study/protocols; L. Swadling, S. Capone., R.A., A.B., R.R., E.N., J.H., C.K., D.B., J.F., A.K., V.A., M.D.S., F.G., M.L.E., L. Siani., C.T., A.H., M.D., A.F., E.B., and P.K., performed the research and analysis; L. Swadling., E.B., A.F., S. Capone, and P.K. wrote the manuscript; E.B. was the principal investigator. Europe PMC Funders Group Europe PMC Funders Author Manuscripts Europe PMC Funders Author ManuscriptsA protective vaccine against hepatitis C virus (HCV) remains an unmet clinical need. HCV infects millions of people worldwide and is a leading cause of liver cirrhosis and hepatocellular cancer. Animal challenge experiments, immunogenetics studies and assessment of host immunity during acute infection highlight the critical role that effective T-cell immunity plays in viral control. In this first-in-man study we have induced antiviral immunity with functional characteristics analogous to those associated with viral control in natural infection, and improved upon a vaccine based on adenoviral vectors alone. We assessed a heterologous prime-boost vaccination strategy based on a replicative defective simian adenoviral vector (ChAd3) and modified vaccinia Ankara (MVA) vector encoding the NS3, NS4, NS5A and NS5B proteins of HCV genotype-1b.Analysis employed single cell mass cytometry (CyTOF), and HLA class-I peptide tetramer technology in healthy human volunteers. We show that HCV specific T-cells induced by ChAd3 are optimally boosted with MVA, and generate very high levels of both CD8+ and CD4+ HCV specific T-cells targeting multiple HCV antigens. Sustained memory and effector T-cell populations are generated and T-cell memory evolved over time with improvement of quality (proliferation and polyfunctionality) following heterologous MVA boost.We have developed a HCV vaccine strategy, with durable, broad, sustained and balanced T-cell responses, characteristic of those associated with viral control, paving the way for the first efficacy studies of a prophylactic HCV vaccine.

Replication defective Adenovirus vectors based on the human serotype 5 (Ad5) have been shown to induce protective immune responses against diverse pathogens and cancer in animal models and to elicit robust and sustained cellular immunity in humans. However, most humans have anti-Ad5 neutralising antibodies that can impair the immunological potency of such vaccines. Here we show that most other human Adenoviruses from rare serotypes are far less potent as vaccine vectors than Ad5 in mice and non-human primates, casting doubt on their potential efficacy in humans. To identify novel vaccine carriers suitable for vaccine delivery in humans we isolated and sequenced over a thousand Adenovirus strains from chimpanzees (ChAd). Replication-defective vectors were generated from different ChAd serotypes and were screened for neutralization by human sera and for ability to grow in human cell lines already approved for clinical studies. Most importantly, we devised a screening strategy to rank the ChAd vectors by immunological potency in mice which predicts their immunogenicity in non-human primates and humans. The vectors studied varied by up to a thousand-fold in potency for CD8 T cell induction in mice. Two of the Europe PMC Funders Group

Ebolavirus disease causes high mortality, and the current outbreak has spread unabated through West Africa. Human adenovirus type 5 vectors (rAd5) encoding ebolavirus glycoprotein (GP) generate protective immunity against acute lethal Zaire ebolavirus (EBOV) challenge in macaques, but fail to protect animals immune to Ad5, suggesting natural Ad5 exposure may limit vaccine efficacy in humans. Here we show that a chimpanzee-derived replication-defective adenovirus (ChAd) vaccine also rapidly induced uniform protection against acute lethal EBOV challenge in macaques. Because protection waned over several months, we boosted ChAd3 with modified vaccinia Ankara (MVA) and generated, for the first time, durable protection against lethal EBOV challenge.

Although merozoite surface protein 1 (MSP-1) is a leading candidate vaccine antigen for blood-stage malaria, its efficacy in clinical trials has been limited in part by antigenic polymorphism and potentially by the inability of protein-in-adjuvant vaccines to induce strong cellular immunity. Here we report the design of novel vectored Plasmodium falciparum vaccines capable of overcoming such limitations. We optimized an antigenic insert comprising the four conserved blocks of MSP-1 fused to tandemly arranged sequences that represent both allelic forms of the dimorphic 42-kDa C-terminal region. Inserts were expressed by adenoviral and poxviral vectors and employed in heterologous prime-boost regimens. Simian adenoviral vectors were used in an effort to circumvent preexisting immunity to human adenoviruses. In preclinical studies these vaccines induced potent cellular immune responses and high-titer antibodies directed against MSP-1. The antibodies induced were found to have growth-inhibitory activity against dimorphic allelic families of P. falciparum. These vectored vaccines should allow assessment in humans of the safety and efficacy of inducing strong cellular as well as cross-strain humoral immunity to P. falciparum MSP-1.